Assessing the Morphological and Mechanical Stability of PEEK in Severe Oilfield Conditions: An Investigation of High-Temperature HCl Acids and Supercritical CO2 Exposure

Abstract This research investigates the aging behavior of Polyetheretherketone (PEEK) when exposed to supercritical CO₂ (scCO2) and acidic environments at elevated temperatures, conditions commonly encountered in the oil and gas industry, specifically downhole applications. With growing interest in replacing traditional carbon steel components, despite PEEK presents a promising alternative due to its superior chemical resistance, thermal stability, and mechanical properties in short term exposure to harsh environment, its aging response (long term exposure) is not well understood. To this end, PEEK was extensively aged at aggressive conditions (high temperature acid and sc-CO2 and evaluated their impact incorporating both the physical, chemical and mechanical response for better understanding of PEEK compatibility for these particular conditions. The study evaluates the long-term performance of PEEK under these harsh conditions through their impact on mechanical, physical and thermal properties. PEEK samples were exposed to HCl at 100°C and in scCO2 at 150°C and 100 bar. After that, samples were analyzed thoroughly utilizing wide variety of characterization techniques to evaluate the uptake and its effect on morphology and mechanical response of PEEK. This study characterized PEEK through multiple analyses, including mechanical testing (hardness, tensile strength), chemical analysis via FTIR, and thermal analysis (DSC) to evaluate crystallinity and providing insights into its structure, properties, and behavior. The findings demonstrate that PEEK offers significant stability when exposed to supercritical CO₂ and HCl at elevated temperatures. Effects of both environments on microstructure and chemistry are elucidated. Phenomena, such as secondary crystallization, are observed while very limited. Mechanical properties, such as elasto-plastic and fracture properties feature also limited modifications. This study reveals that exposure to HCl induces subtle plasticisation effects in PEEK, unlike scCO2 which yields no such plasticisation effects. Importantly, both aging conditions trigger solely physical modifications, altering the material's morphological, mechanical, and thermal characteristics without inducing significant chemical interaction that could lead to alter or generating new functional groups. This research contributes valuable insights for the oil and gas industry, promoting the adoption of PEEK as a viable replacement for carbon steel in applications where long-term material resilience is critical, particularly in CO2 transport, storage and well treatment processes.